1. Field of the Invention
This invention relates to rolling element spacers for various types of rolling guide units, such as a linear guide unit, a ball screw unit and the like provided with an endless circulating passage for rolling elements, such as balls and rollers, the rolling elements being adapted to be interposed between adjacent rolling elements in the endless circulating passage, reduce the abrasion and generation of heat of the rolling elements and smooth the rolling of the rolling elements.
2. Description of the Related Art
The known rolling guide units in which a pair of members make relative movements continuously via a row of endlessly circulating balls and rollers include a linear guide unit used in a linear guide portion of a machine tool and a transfer apparatus and adapted to guide a movable member, such as a table on a fixed portion, such as a bed or a saddle; and a ball screw used with this linear guide unit and adapted to give strokes of linear movements to the movable member in accordance with an amount of rotations of a motor.
The first-mentioned linear guide unit includes a track rail provided on such a fixed portion as mentioned above and having rolling surfaces, which extend in the longitudinal direction, for the rolling elements; and a slide block which has load rolling surfaces opposed to the rolling surfaces of the track rail via plural rolling elements, and which is provided with endless circulating passages for the rolling elements rolling on these load rolling surfaces, the movable member-supporting slide block being moved linearly and continuously along the track rail. Conversely, some linear guide units are formed so that a track rail is moved with respect to a fixed slide block.
The second-mentioned ball screw includes a screw shaft provided with a helical ball rolling groove formed at a predetermined lead angle; and a nut member having a load rolling groove opposed to the ball rolling groove via plural balls, and provided with an endless circulating passage for the balls rolling on this load rolling groove; the balls being circulated in the endless circulating passage in accordance with the relative rotational movements of these screw shaft and nut member, the nut member and screw shaft being thereby moved relatively in the axial direction.
In such rolling guide units, a rolling element, such as each of the balls and rollers circulating in the endless circulating passage contacts the rolling elements positioned on the front and rear sides thereof. Therefore, when the rolling guide units are used at a high speed, there is the possibility that the rolling elements wear comparatively early due to the mutual abrasion of, for example, the rolling elements, and that the rolling elements and load rolling surface seize due to frictional heat. When the moving direction is reversed, i.e., when the direction in which the rolling elements are circulated is reversed, the arrangement of the rolling elements in the endless circulating passages is liable to get out of order. In an extreme case, a so-called locking phenomenon in which the rolling elements stop up in the endless circulating passage occurs, so that there is the possibility that the rolling guide unit itself becomes inoperable. Japanese Patent Laid-Open No. 315835/1999 discloses as a rolling guide unit adapted to eliminate these drawbacks a rolling guide unit in which rolling element spacers are interposed between rolling elements adjacent to each other in an endless circulating passage.
In the rolling guide unit disclosed in this publication, rolling element spacers of a synthetic resin called xe2x80x9cseparatorxe2x80x9d are arranged alternately with balls in an endless circulating passage, and the contact of one ball with another is thereby prevented. Such separators are formed in the shape of a disc the outer diameter of which is smaller than the diameter of the balls, and provided on both the front and rear surfaces thereof with ball retaining seats the radius of curvature of which is larger than that of the spherical surface of each ball. When the balls and separators are thereby arranged alternately without causing clearances to occur in the endless circulating passage, each ball is held between a pair of separators adjacent to front and rear sides thereof. Accordingly, even when the direction in which the balls are circulated is reversed, the balls are circulated with the separators in the endless circulating passage without causing the row of the balls and separators to be disordered.
However, when the ball retaining seats slidingly contacting the balls are formed concavely to a radius of curvature larger than that of the spherical surface of each ball just as those of the rolling element spacer disclosed in Japanese Patent Laid-Open No. 315835/1999, clearances occur between a circumferential portion of the ball retaining seat and balls, and the balls shake with respect to the rolling element spacers. Therefore, the meandering of the balls in the endless circulating passage cannot be completely eliminated.
From the viewpoint of the prevention of the meandering of the balls in the endless circulating passage, it is necessary that the balls settle without being shaken on the ball retaining seats of the rolling element spacers. In order to meet the requirement, it is necessary that the ball retaining seats be formed so as to have concave surfaces which are substantially in conformity with the spherical surfaces of the balls. However, when the ball retaining seats are formed so as to have such concave surfaces, the contact surface area of each ball and a relative ball retaining seat becomes large. This causes a fear that an increase in the slide contact resistance of the rolling element spacers with respect to the balls, early wear on the rolling element spacers, etc. occur.
The present invention has been made in view of the above-mentioned circumstances, and provides rolling element spacers capable of improving the stability of rolling elements with respect to retaining seats to a high level, stabilizing the alignment of the rolling elements and rolling element spacers in endless circulating passages, and reducing the slide contact resistance exerted on the rolling elements.
According to an aspect of the present invention, the rolling element spacers used for a rolling guide unit in which a pair of members make relative continuous movements via rows of endlessly circulating rolling elements, interposed between adjacent rolling elements in endless circulating passages and circulated with the rolling elements therein, have a pair of retaining seats respectively which the rolling elements slidingly contact, each retaining seat and a relative rolling element contacting each other on rolling element cutting planes perpendicular to the axis of rotation thereof, at only the two portions of the retaining seat which are in the vicinity of both ends thereof.
According to such technical devices, each retaining seat and a relative rolling element contact each other on rolling element cutting planes perpendicular to the axis of rotation thereof, at only the two portions of the retaining seat which are in the vicinity of both ends thereof. Therefore, the spherical surface of a ball or the outer circumferential surface of a roller fits in a stable condition in a relative retaining seat, and the seating condition of the rolling element with respect to the retaining seat becomes stable. Accordingly, when such rolling element spacers and rolling elements are arranged alternately in the endless circulating passages in a rolling guide unit, the alignment of these rolling elements and rolling element spacers are stabilized, and the meandering of the rolling elements in the endless circulating passages can be prevented.
On the rolling element cutting planes perpendicular to the axis of rotation thereof, each retaining seat and a relative rolling element contact each other at only the two portions in the vicinity of both ends of the retaining seat. For example, when the rolling element is a ball, the ball and a relative retaining seat contact each other annularly. Namely, since the center of each retaining seat and the relative rolling element are in a non-contacting state, it becomes possible to minimize the contact area of the retaining seat and rolling element, and thereby reduce the slide contact resistance exerted on the rolling element.
Moreover, according to the present invention, the center of each retaining seat and a relative rolling element are in a non-contacting state, and the center of each retaining seat does not contribute at all to the alignment of the rolling elements. Therefore, a communication through hole extending between the retaining seats can be provided, and this communication hole can be utilized as a lubricating oil reservoir.
In a ball screw unit, the rolling speed of balls held between a helically formed load rolling groove of a nut and a ball rolling groove of a screw shaft varies finely due to errors of formation of these grooves, so that a distance between the balls rolling as they impart a load to the groove of the nut also varies. Therefore, when the rolling element spacers have a high rigidity in the rolling element arranging direction, the balls and rolling element spacers are put in a forcibly pushing state with respect to one another in the endless circulating passage at the time of the occurrence of a decrease in the distance between the balls due to the above-mentioned reasons, and the balls are stopped up in the endless circulating passage. Consequently, in view of the necessity of absorbing a fine variation of the distance between the adjacent balls, it is preferable to give an elasticity to the rolling element spacers in the rolling element arranging direction by forming grooves in outer circumferential surfaces surrounding the circumferences of the retaining seats.
As has been described above, according to the rolling element spacers of the present invention, the spherical surfaces of the balls or the outer circumferential surfaces of the rollers fit stably in the retaining seats, and the seating condition of the rolling elements with respect to the retaining seats becomes stable. Since the center of each retaining seat and a relative rolling element are in a non-contacting state, it becomes possible to reduce the contact area of each retaining seat and a relative rolling element, improve the seating condition of the rolling elements with respect to the retaining seats, stabilize the alignment of the rolling elements and rolling element spacers in an endless circulating passage, and reduce a slide resistance exerted on the rolling elements.